Zinc oxide production methods are divided into two major categories: water law and fire law.
First, the water law
The water method is to leaching various zinc oxide ore, zinc-containing soot and other zinc-containing materials by using acid, alkali or ammonia carbonate solution. The purified zinc oxide is obtained by removing impurities from the liquid, precipitating basic zinc carbonate, drying and calcining. Water produced zinc oxide, also known as active zinc oxide. The former Soviet Union, Germany, Japan, and other countries all have production. China's Tianjin, Shanghai, Sichuan, Hebei and other provinces and municipalities have production, but their output is very small and there is no industrial scale.
Second, the fire method
Fire law is divided into two kinds: direct law (American law) and indirect law (French law).
The direct method is to add sulphidic zinc concentrate by boiling and roasting, adding carbonaceous reducing agent to make pellets (in some cases not forming pellets) and adding Wethel. At high temperatures, zinc is reduced and immediately oxidized by CO2 in the furnace gas and oxygen in the incoming air. After cooling, it enters the baghouse to obtain finished zinc oxide (containing 99.5% of ZnO). This method can also be used to treat low-grade zinc oxide ore, or various zinc-containing residues, such as flat tank zinc slag, vertical tank zinc slag, and other external zinc oxide production (generally containing ZnO 90% to 95%).
The indirect method is to melt the metal zinc ingot and add it to the evaporation furnace. At high temperature, zinc is evaporated and introduced into the oxidation furnace (room) to be oxidized. After cooling, it is put into a baghouse to obtain finished product zinc oxide (including ZnO 9917%).
The indirect method is widely used, and the annual output of zinc oxide in China is about 70% of the total amount of zinc oxide. Indirect methods can be divided into man-slot furnaces, crucible furnaces, rectification furnaces, and reverberatory furnaces due to the differences in production equipment. The most commonly used are the latter three methods of production.